1. Field of the Invention
Aspects of the present invention relate generally to an image forming apparatus and an image quality enhancement method thereof, and more particularly, to an image forming apparatus and an image quality enhancement method thereof that improves image quality by determining the presence or absence of an edge area based on the pattern comparison between a plurality of subwindows, and determining a dot size of a center reference pixel depending on the presence or absence of the edge area.
2. Description of the Related Art
Generally, a monochrome laser printer or a color laser printer conducts gray representation to express an image, dividing one pixel into a plurality of subpixels. It takes a considerable amount of data to process one pixel based on a plurality of gray levels (multi-gray-levels). Increased amount of data results in an increased time to transmit the data from a computer to a laser printer and in a requirement for increased memory capacity. Accordingly, halftoning is used to mitigate this problem. In halftoning, pixels are generally processed to be on or off, in one-bit processing.
However, because the halftoning simply represents dots or pixels in on or off states, images still tend to look rough. The problem is more severe in relatively bright regions. A 1-bit-gray processing has been adopted to deal with such problems. A method to generate multi-levels of data from 1-bit data is disclosed in several previous publications, including Korean Patent Registration No. 0538244 and US Patent Publication No. 2005-0141037. These publications generally disclose a method to determine whether a window is an edge area, and if not, to generate a level according to the number of dots of the surrounding pixels. This method will be explained in detail below with reference to FIG. 1.
As shown in FIG. 1, a dithering mask, an LPI (lines per inch) and an angle of the dithering mask, and a binary image are input at operation S110. A window of a predetermined size is created based on these input values at operation S120, and the presence of an edge area is determined at operation S130. Based on the pixels of a binary image where a window is applied, a maximum value is detected from among the dithering mask values of a white region where there is no dot printed, and a minimum value is detected from among the dithering mask values of a black region where there is dots printed.
A smooth area is determined if the maximum value of the white region is greater than the minimum value of the black region. An edge area is determined if the maximum value of the white region is greater than the minimum value of the black region, and if a difference between the two values is greater than a threshold. A smooth area is determined if the difference between the maximum value of the white region and the minimum value of the black region is less than the threshold.
Image enhancement is performed with respect to the smooth area at operation S140, and dot size is determined at operation S150. Accordingly, a pulse signal is applied to the LSU at operation S160 according to the determined dot size. No image enhancement is performed if the edge area is detected at operation S130.
As described above, a conventional image forming apparatus requires a dithering mask to determine the presence of an edge area. In a color representation, a plurality of dithering masks are required to correspond to respective colors, so it consumes significant memory resources. Furthermore, because images are enhanced only on the smooth areas, edges sometimes appear fuzzy depending on the dot pattern. Therefore, brightness adjustment is required to take the characteristics of edge area into consideration